Impeller for a centrifugal slurry pump

ABSTRACT

A improved impeller for use in a centrifugal slurry pump is provided, comprising: a top shroud; a bottom shroud; and a middle portion therebetween, said middle portion having at least one substantially vertical wall defining a slurry flow channel, wherein the top shroud, bottom shroud and middle portion are configured as one piece to together define a first unitary body; at least one vane nose positioned at a leading edge of the at least one substantially vertical wall; and, optionally, a retaining ring mounted over the top shroud to secure the vane nose within the body.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 14/066,487, filed Oct. 29, 2013, which claimed priority to U.S. Provisional Application 61/720,122 filed Oct. 30, 2012, the entire contents of both which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to an improved impeller for a centrifugal slurry pump.

BACKGROUND OF THE INVENTION

A conventional centrifugal slurry pump generally includes an impeller having multiple vanes and which is mounted for rotation within a volute casing. The slurry pump imparts energy to the slurry through the centrifugal force produced by rotation of the impeller. The slurry enters into the impeller through an intake conduit positioned in line with the rotating axis and is accelerated by the impeller, flowing radially outward into the volute casing and subsequently exiting through a discharge conduit. A suction sideliner is positioned a predetermined short distance away from the impeller suction side, the distance being so small as to substantially preclude slurry flow between the impeller and the suction sideliner.

Slurries are two-phase mixtures of solid particles and fluids in which the two phases do not chemically react with each other and can be separated by mechanical means. Slurries are typically characterized as either non-settling or settling in accordance with the size of the solid particles suspended within the fluid. Non-settling slurries include fine particles (less than 50 μm) which form stable homogeneous mixtures. Settling slurries include coarse particles (greater than 50 μm) which form an unstable heterogeneous mixture. Examples of slurries include oil/water; tailings/water; and coke/water slurries. Such slurries can cause abrasion, erosion, and corrosion, resulting in significant wear to pump parts.

Attempts have been made to reduce wear of the pump parts, particularly the impeller, volute casing, and suction sideliner. A slurry pump operating at low speeds outlasts a faster running pump. Slower running pumps generally have heavier, larger diameter impellers to spread the energy which causes the wear over a larger area. Various modifications related to the configuration, thickness, number, and arrangement of impeller vanes have been described. For example, thicker impeller vanes are capable of handling an abrasive slurry and minimizing wear, but necessitate a reduction in vane number to avoid narrowing the passageways through which the slurry flows.

Pump parts have been formed of various hard metals, elastomeric, or metal-reinforced elastomeric materials to suit the material being pumped. Rubber-lined pumps are often used for pumping non-settling slurries since the resilience of the rubber can absorb and return the energy generated by the impact of the particles to the slurry; however, rubber-lined pumps can be damaged by sharp, large particles or degraded by hydrocarbons. Metal slurry pumps are suitable for pumping abrasive, settling slurries, with 28% chrome iron being the most common material and stainless steel being used for corrosive slurries. The performance of a chrome impeller may be enhanced by laser cladding which deposits an alloy coating to the surfaces of the impeller.

Among all pump parts, the impeller greatly influences the flow patterns of the slurry and the rate of wear. The average lifespan of an impeller is about 1,500 to 2,000 hours, which approximates only half the lifespan of the slurry pump itself. During manufacture, an impeller is typically cast as one piece; thus, for replacement, an entirely new impeller needs to be installed. The maintenance hours and downtime of the pump are time and cost consuming. Increasing the lifespan of the impeller would be greatly beneficial in maintaining pump performance and meeting production targets.

Accordingly, there is a need for an improved impeller for a centrifugal slurry pump.

SUMMARY OF THE INVENTION

In one aspect, the invention may comprise an impeller for a centrifugal slurry pump, which may comprise:

-   -   a top shroud; a bottom shroud; and a middle portion         therebetween, said middle portion having at least one         substantially vertical wall defining a slurry flow channel,         wherein the top shroud, bottom shroud and middle portion are         configured as one piece to together define a first unitary body;     -   at least one vane nose positioned at a leading edge of the at         least one substantially vertical wall;     -   an inner retaining ring mounted over the top shroud to secure         the vane nose within the body; and     -   an outer wear ring mounted on a periphery of the top shroud.

In one embodiment, the first unitary body, the at least one vane nose, the inner retaining ring, and the outer wear ring are manufactured as four separate pieces. In another embodiment, the at least one vane nose and the inner retaining ring are configured as one piece to together define a secondary unitary body and, thus, the impeller consists of a first unitary body, a second unitary body, and an outer wear ring, each manufactured separately from the other and assembled together to form the impeller.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring to the drawings wherein like reference numerals indicate similar parts throughout the several views, several aspects of the present invention are illustrated by way of example, and not by way of limitation, in detail in the figures, wherein:

FIG. 1 is a cutaway sectional view showing a centrifugal pump for mineral slurry within which the impeller of the present invention can be used.

FIG. 2 is a sectional side view of one embodiment of an impeller comprising multiple components.

FIG. 3 is a detailed view of a bottom shroud and middle portion of one embodiment of the impeller as shown in FIG. 2, without a vane nose attached.

FIG. 4 is a view of the vane nose of the impeller as shown in FIG. 2.

FIG. 5 is a bottom view of the inner retaining ring of the impeller as shown in FIG. 2.

FIG. 6 is a sectional side view of a portion of the inner retaining ring of FIG. 4 when fastened to the top shroud.

FIG. 7 is a detailed view of a bottom shroud and middle portion of FIG. 3, with a vane nose attached.

FIG. 8 is a sectional side view of a vane nose and tail formed of different materials.

FIG. 9 is a perspective view of the inner retaining ring when mounted over the vane nose and body of the impeller as shown in FIG. 7.

FIG. 10 is a perspective view of another embodiment of a vane nose useful in an impeller of the present invention.

FIG. 11 is a perspective view of another embodiment of an impeller comprising multiple components.

FIG. 12 is a perspective view of the impeller as shown in FIG. 11 where the vane nose and inner retaining ring have been removed.

FIG. 13 is a side view of the vane nose and inner retaining ring configured as one piece to define a unitary body.

FIG. 14 is a perspective view of an alternative embodiment of the present invention, including an outer wear ring.

FIG. 15 is a perspective view of yet another alternative embodiment of the present invention, including an outer wear ring.

FIG. 16 is a perspective view of yet another alternative embodiment of the present invention, including an outer wear ring.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In one aspect, the invention comprises an impeller which is assembled from multiple components, rather than casting the impeller as a single component as is commonly done. Each component may thus be individually tailored to its specific function in the impeller.

The components of the impeller may be readily and conveniently connected or detached for inspection, reinsertion or replacement if necessary. This obviates the current need to replace an entirely new impeller; decreases the maintenance hours and downtime of the pump; and increases the lifespan of the impeller.

The present invention relates generally to an impeller for use in a centrifugal slurry pump. An embodiment of a centrifugal slurry pump 100 wherein an impeller of the present invention can be used is shown in cross-section in FIG. 1. The centrifugal pump 100 is driven by a motor (not shown), such as electric motor, turbine, etc., that is connected to an impeller of the present invention by a shaft 172. The impeller 110 is provided in a volute casing 174. An intake conduit 176 is provided in the volute casing 174 to route liquid into the pump 100, where the liquid will be subsequently discharged from the pump 100 through a discharge conduit 178 provided in the volute casing 174. A suction sideliner 180 is provided to allow access to the inside of the volute casing 174. Rotation of the impeller 110 causes slurry within the volute casing 174 to be accelerated radially from the intake conduit 176 and discharged circumferentially at increased pressure at pump outlet, discharge conduit 178, in a manner well understood by those skilled in the art.

One embodiment of an impeller 10 of the present invention is shown in FIGS. 2 to 9. Impeller 10 includes a body 12, at least one vane nose 14, and an inner retaining ring 16. The body 12 has an annular and cylindrical shape which defines various directions with respect to the shape. As used herein, the term “radially” refers to a direction which is generally along an imaginary radius of the annular and cylindrical shape. As used herein, the term “axially” refers to a direction which is generally parallel to the axis of rotation. As used herein, the term “circumferentially” refers to a direction which is generally along an imaginary circumference of the annular and cylindrical shape.

The body 12 has a top shroud 18, a bottom shroud 20, and a middle portion 22 sandwiched between the top and bottom shrouds 18, 20. The body 12 defines an axially-disposed eye 24. As used herein, the term “eye” means the center of the impeller 10 where the slurry enters. The eye 24 is coaxial with the central axis which is the axis of rotation of the impeller 10.

The top shroud 18 comprises a disc which defines at least one vane tail 26. Multiple vane tails 26 are spaced circumferentially about the central axis, and evenly apart from each other. The top shroud 18 has at least one hole 28 dimensioned to receive a fastener 30 which is inserted to secure the retaining ring 16 to the top shroud 18. In one embodiment, the retaining ring 16 is secured to the top shroud 18 using screw fasteners and also bonded with an epoxy. Alternatively, the retaining ring 16 may be secured to the top shroud 18 by brazing or hot isostatic pressing. Multiple holes 28 may be spaced circumferentially and evenly apart from each other. The top shroud 18 defines a first recess 32 which is configured to receive and accommodate a corresponding protrusion 34 of the retaining ring 16. The dimensions of the first recess 32 are not essential to the invention and are dictated by the size of the protrusion 34.

The bottom shroud 20 comprises a disc having an axially-disposed hub 36 extending from the bottom shroud 20. The hub 36 is operatively connectable to a drive shaft (not shown) for causing rotation of the impeller 10 about its central axis.

The middle portion 22 comprises at least one wall 38 which defines a passageway 40 through which the slurry flows. The wall 38 defines a second recess 42 which is configured to receive and accommodate the vane nose 14. The dimensions of the second recess 42 are not essential to the invention and are dictated by the size and configuration of the vane nose 14.

The vane nose 14 comprises a nose body 44 and upper and lower ends 46, 48, respectively, at opposite ends of the nose body 44. The nose body 44 is preferably curved in order to direct slurry flow. In one embodiment, the nose body 44 is substantially rectangular in shape. The upper end 46 defines a tab 50 which extends upwardly to engage a complementary slot 52 defined within the retaining ring 16. An elongate side tab 54 projects from the nose body 44 beyond each of the upper and lower ends 46, 48 to insert into the second recess 42 defined by the wall 38. The configuration of the vane nose 14 may be varied so as to ensure that it inserts into, and is retained, by the second recess 42. In one embodiment, the side tab 54 is substantially square or rectangular. The vane nose 14 is positioned in an orientation that is inclined at an angle less than 90 degrees relative to the bottom shroud 20. The angle may range from about 45 degrees to less than about 90 degrees

The inner retaining ring 16 comprises a disc having a top side 56, an underside 58, and defining an opening 60. The retaining ring 16 defines at least one slot 52 sized and configured to engage the corresponding tab 50 of the vane nose 14. In one embodiment, the retaining ring 16 has four slots 52. The retaining ring 16 has at least one aperture 62 through which a fastener 30 can extend into contact with a corresponding hole 28 of the top shroud 18 to secure the retaining ring 16 to the top shroud 18. Multiple apertures 62 may be spaced circumferentially and evenly apart from each other.

On the top side 56, the retaining ring 16 has at least one vane tail extension 64 which aligns with a corresponding vane tail 26 of the top shroud 18 to complete the length of the vane tail 26. The vane tail 26 may also be referred to as an expeller vane. The expeller vanes 26 may provide some additional pump efficiency and assist in moving particles out from between the impeller and the suction liner.

On the underside 58, the retaining ring 16 has at least one protrusion 34 sized and configured to fit securely within the first recess 32 of the top shroud 18. When mounted to the top shroud 18, the protrusion 34 surrounds the upper end 46 of the vane nose 14 to restrain the vane nose 14 within the body 12.

Suitable fasteners include, any suitable system or component that can be driven, screwed, or otherwise forced through the holes 28 and apertures 62 to attach the retaining ring 16 to the top shroud 18, including without limitation, bolts, screws, rivets, or any other fasteners commonly used in construction. Although less preferred, it is also contemplated that the retaining ring 16 may be attached to the top shroud 18 via other means, such as for example, other fastening mechanisms or adhesives. If desired, the retaining ring 16 can be permanently attached such as by brazing, hot isostatic pressing or other suitable means known to those skilled in the art.

The impeller 10 can be constructed from any material or combination of materials having suitable properties such as, for example, mechanical strength; erosion, corrosion and wear resistance; ability to withstand severe applications; and ease of machining. The body 12, vane nose 14, and retaining ring 16 may be formed of cermets (such as but not limited to tungsten carbide), metal matrix composites (such as but not limited to tungsten carbide in a metal matrix), hard metal alloys, metal-reinforced elastomers, ceramic-reinforced elastomers (such as but not limited to alumina or tungsten carbide in a urethane or rubber) or elastomers. Suitable materials include, but are not limited to, aluminum, brass, bronze, cast iron, composite, plastic, rubber, stainless steel, titanium, or other appropriate materials known to those skilled in the art.

It is well known that the leading edges of impeller vanes are most severely worn among all components of a typical centrifugal slurry pump. As used herein, the term “leading edge” means the surface which faces in a direction of rotation of the impeller. As used herein, the term “trailing edge” means the surface which faces in a direction that is opposite the direction of rotation of the impeller. In one embodiment, the vane nose 14 is preferably formed of tungsten carbide, while the wall 38 is formed of chromium white iron. In one embodiment, the body 12 is formed of chromium white iron. Thus, by being able to make the vane nose 14 of a stronger material than the single body 12, which includes wall 38, longer wear life of the impeller can be expected.

The “inner circle” of the top shroud of common impellers is greatly prone to damage and wear. The retaining ring 16 protects this portion of the impeller 10. In one embodiment, the retaining ring 16 is formed of chromium white iron.

The fasteners 30 such as for example, screws, pins, or bolts, may be formed of steel, for example, stainless steel, and strength-bearing materials.

It will be appreciated that the impeller 10 is simple but rugged in construction that it can be made at low cost and easily fabricated. The body 12 is preferably of one-piece construction combining the top shroud 18, bottom shroud 20, and middle portion 22, and may be formed by any suitable manufacturing process including, but not limited to, casting, machining, hot isostatic pressing, cast infiltration and other processes known in the art. In a casting process, liquid material of which the body 12 is to be formed is fed into a mold cavity where it cools and hardens to the configuration of the cavity. Once the material has hardened, the finished body 12 is released from the mold. Casting is a relatively simple and rapid process for producing the body 12. The retaining ring 16 may be manufactured similarly to the body 12. Machining may be used to form the holes 28, apertures 62, and recesses 32, 42. In one embodiment, the vane nose 14 may be formed by sintering or hot isostatic pressing, whereby powdered material is held in a mold and heated to fuse the material together into a single piece.

During assembly of the impeller 10, the vane nose 14 is mounted within the body 12 by inserting the side tab 54 into the second recess 42 (FIG. 6). Multiple vane noses 14 are inserted within the body 12 so as to be spaced circumferentially about the central axis, and to define flow channels 66. Positioning of the vane noses 14 between the eye 24 and outside diameter of the impeller 10 allows the vane noses 14 to direct slurry flow.

The retaining ring 16 is mounted over the top shroud 18 to fit the protrusion 34 within the first recess 32, to align the slot 52 with the tab 50 of the vane nose 14, and to align the apertures 62 with the corresponding holes 28 of the top shroud 18 (FIG. 8). At least one fastener 30 is passed through the aperture 62 and hole 28 to attach the retaining ring 16 to the top shroud 18, thereby securing the vane nose 14 in place within the middle portion 22 of the body 12 (FIG. 5). The retaining ring 16 can be readily attached to or released from the top shroud 18 of the body 12 as needed.

In another embodiment, the vane nose 14 can be manufactured without tabs 50 and 54 and the body 12 will not have slot 52 sized and configured to engage the corresponding tab 50 or slot 42 sized and configured to engage the corresponding tab 54. This embodiment is shown in FIG. 10, where vane nose 114 comprises a nose body 144 and upper and lower ends 146, 148, respectively, at opposite ends of the nose body 144. The front surface 141 may be curved in order to direct slurry flow. The back surface 143, however, is essentially planar, so that the vane nose 114 can be attached to a now flat surface of body 12, which no longer has slot 52, by glue such as epoxy and the like. Similarly, upper end 146 is essentially planar or slightly concave so as to be able to be attached to the surface of body 12, which no longer has slot 42, by glue such as epoxy and the like. Other means for fastening two pieces of metal together, such as but not limited to brazing or hot isostatic pressing, as known in the art can also be used. In one embodiment, the vane nose 14 or 114 is manufactured as a single body.

Another embodiment of an impeller of the present invention is shown in FIGS. 11-13. Impeller 210 includes a body 212, at least one vane nose 214, and an inner retaining ring 216. The body 212 has an annular and cylindrical shape which defines various directions with respect to the shape. The body 212 (shown independently in FIG. 12) has a top shroud 218, a bottom shroud 220, and a middle portion 222 sandwiched between the top and bottom shrouds 218, 220. The body 212 defines an axially-disposed eye 224. The top shroud 218 comprises a disc which defines at least one vane tail 226. Multiple vane tails or expeller vanes 226 are spaced circumferentially about the central axis, and evenly apart from each other.

In one embodiment, the top shroud 218 defines a first recess 232 which is configured to receive and accommodate inner retaining ring 216.

The bottom shroud 220 comprises a disc having an axially-disposed hub 236 (shown in FIG. 12) extending from the bottom shroud 220. The hub 236 is operatively connectable to a drive shaft (not shown) for causing rotation of the impeller 210 about its central axis. The bottom shroud also comprises a cut-out portion 221 for accommodating a vane nose assembly 290, which assembly is shown in FIG. 13. The middle portion 222 comprises at least one wall 238 which defines a passageway 240 through which the slurry flows. The wall 238 is designed to accommodate the vane nose 214 of vane nose assembly 290.

With reference specifically to FIG. 13, the vane nose assembly 290 is a unitary body comprising vane nose 214, retaining ring 216 and hub cover 215, which hub cover 215 is designed to fit into cut-out portion 221 of bottom shroud 220. The vane nose assembly 290 is designed to be set, for example, by epoxy, into body 212. Thus, in this embodiment, vane nose assembly 290 can be made from a stronger material than body 212. Thus, the regions of the impeller that are generally more greatly exposed to the abrasive slurry can be manufactured as a single unit out of stronger wear-resistant material. Thus, the slurry pump life-time can be greatly extended.

In another embodiment, wear and damage to the expeller vanes 26 or 226 may be mitigated by different strategies. In one example, the expeller vanes 26 226 may be protected using attached wear elements such as carbide tiles or coating the expeller vanes with a wear-resistant coating, such as by thermal spraying, laser cladding, hot isostatic pressing or other techniques well known to those in the art.

In one embodiment, the expeller vanes 26 or 226 may be eliminated and the retaining ring 16 may comprise a hard or wear-resistant material. The retaining ring 16 may be formed from a plurality of carbide tile segments 301 which are assembled to form a complete ring, as is shown in FIG. 14.

In one embodiment, where expeller vanes are eliminated, an outer wear ring 302 may be attached or otherwise formed into the impeller. The outer wear ring may also be formed from a plurality of carbide tile segments 303, as is shown in FIG. 14.

Hard or wear-resistant material may include such materials as ceramic or non-ceramic carbides such as chromium carbide, tungsten carbide, or a cermet such as sintered tungsten carbide. Sintered tungsten carbide, also known as cemented carbide, is a composite material comprising tungsten carbide powder mixed with a binder metal such as cobalt or nickel, compacted in a die and then sintered at a very high temperature. Wear-resistant materials may also include various ceramic materials such as alumina or a nitride such as silicon nitride. As used herein, a ceramic material is an inorganic, non-metallic, oxide, nitride or carbide material, which may or may not be crystalline. Suitable hard or wear-resistant materials are well known in the art and are readily commercially available.

In an alternative embodiment, as shown schematically in FIG. 15, the impeller may include an inner retaining ring 16 formed from a plurality of segments 401 which are separated by small gaps and a outer wear ring 402 also formed from a plurality of segments 403, also separated by small gaps. The gaps of the inner ring 16 and the gaps of the outer ring 402 are connected by grooves 404 formed in the top shroud 18 to form channels which mimic the function of expeller vanes.

In another embodiment, as shown in FIG. 16, the inner and outer rings may be dimensioned to abut each other, such that the top shroud is completely covered and not exposed. Alternatively, the inner and outer rings may be combined into a single wear resistant disk which covers the top shroud 18. The element which covers the top shroud, whether formed from abutting inner and outer rings, or a unitary element, may comprise expeller vanes or grooves which mimic the function of expeller vanes. This single wear resistant disk may be formed by hot isostatic pressing, cast infiltration or a similar suitable technique.

DEFINITIONS AND INTERPRETATION

The singular forms “a,” “an,” and “the” include plural reference unless the context clearly dictates otherwise. It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for the use of exclusive terminology, such as “solely,” “only,” and the like, in connection with the recitation of claim elements or use of a “negative” limitation. The terms “preferably,” “preferred,” “prefer,” “optionally,” “may,” and similar terms are used to indicate that an item, condition or step being referred to is an optional (not required) feature of the invention.

The term “and/or” means any one of the items, any combination of the items, or all of the items with which this term is associated.

As will also be understood by one skilled in the art, all language such as “up to”, “at least”, “greater than”, “less than”, “more than”, “or more”, and the like, include the number recited and such terms refer to ranges that can be subsequently broken down into sub-ranges which fall within the broader range. In the same manner, all ratios recited herein also include all sub-ratios falling within the broader ratio.

One skilled in the art will also readily recognize that where members are grouped together in a common manner, such as in a Markush group, the invention encompasses not only the entire group listed as a whole, but each member of the group individually and all possible subgroups of the main group. Additionally, for all purposes, the invention encompasses not only the main group, but also the main group absent one or more of the group members. The invention therefore envisages the explicit exclusion of any one or more of members of a recited group. Accordingly, provisos may apply to any of the disclosed categories or embodiments whereby any one or more of the recited elements, species, or embodiments, may be excluded from such categories or embodiments, for example, as used in an explicit negative limitation.

As will be apparent to those skilled in the art, various modifications, adaptations and variations of the foregoing specific disclosure can be made without departing from the scope of the invention claimed herein. The various features and elements of the invention described herein may be combined in a manner different than the specific examples described or claimed herein without departing from the scope of the invention. In other words, any element or feature may be combined with any other element or feature in different embodiments, unless there is an obvious or inherent incompatibility between the two, or it is specifically excluded. 

We claim:
 1. An impeller for use in a centrifugal slurry pump comprising: (a) a top shroud; a bottom shroud; and a middle portion therebetween, said middle portion having at least one substantially vertical wall defining a slurry flow channel, wherein the top shroud, bottom shroud and middle portion are configured as one piece to together define a first unitary body; (b) at least one vane nose positioned at a leading edge of the at least one substantially vertical wall; (c) a retaining ring mounted over the top shroud to secure the vane nose within the body; and (d) an outer wear ring mounted on a periphery of the top shroud.
 2. The impeller of claim 1, wherein the vane nose comprises a first material and the first unitary body comprises a second material different from the first material.
 3. The impeller of claim 1, wherein the vane nose is formed of sintered tungsten carbide.
 4. The impeller of claim 1, wherein the first unitary body is formed of chromium white iron.
 5. The impeller of claim 1, wherein the vane nose comprises a curved nose body, and upper and lower ends.
 6. The impeller of claim 5, wherein the upper end defines an upwardly extending tab for engaging a slot of the retaining ring.
 7. The impeller of claim 5, wherein an elongate side tab projects from the nose body beyond each of the upper and lower ends for insertion into a recess formed within the at least one substantially vertical wall of the middle portion.
 8. The impeller of claim 7, wherein the vane nose is inserted into the recess in an orientation that is inclined at an angle less than 90 degrees relative to the bottom shroud.
 9. The impeller of claim 1, wherein the top shroud defines a recess configured to receive at least one protrusion of the retaining ring.
 10. The impeller of claim 9, wherein the retaining ring and top shroud comprise at least one corresponding aperture for receiving a fastener therethrough to attach the retaining ring to the top shroud.
 11. The impeller of claim 10, wherein the bottom shroud comprises a disc having a hub operatively connectable to a drive shaft for causing rotation of the impeller about a central axis.
 12. The impeller of claim 1, wherein the first unitary body, the at least one vane nose and the retaining ring are each manufactured individually.
 13. The impeller of claim 1, wherein the at least one vane nose and the retaining ring are configured as one piece to together define a secondary unitary body.
 14. The impeller of claim 13, wherein the first unitary body comprises a first material and the second unitary body comprises a second material different from the first material.
 15. The impeller as claimed in claim 14, wherein the second unitary body further comprises a hub cover.
 16. The impeller of claim 1 wherein either or both the retaining ring and the outer wear ring comprise a hard or wear-resistant material.
 17. The impeller of claim 16 wherein either or both the retaining ring and the outer wear ring comprise a plurality of carbide segments affixed to the top shroud.
 18. The impeller of claim 17 wherein both the retaining ring and the outer wear ring comprise a plurality of carbide segments, each separated by a gap, wherein the gaps are connected by a groove formed in the top shroud to mimic the function of an expeller vane.
 19. The impeller of claim 1 wherein the retaining ring and the outer wear ring abut each and completely cover the top shroud.
 20. The impeller of claim 19 wherein the retaining ring and the outer wear ring are comprised in a unitary element.
 21. The impeller of claim 20 wherein the unitary retaining ring and outer wear ring comprises a single carbide tile.
 22. The impeller of claim 21 wherein the unitary retaining ring and outer wear ring comprise expeller vanes or groove which mimic the function of expeller vanes. 